Question

I have some TreeView’s in my winform application. I am trying to make mass changes to all of them in one go. So I wrote the code below:

private void ResetTreeViewColors()
{
    foreach (TreeView tv in this.Controls)
    {
        foreach(TreeNode tn in tv.Nodes)
        {
            tn.BackColor = Color.White;
            tn.ForeColor = Color.Black;
        }
    }
}

it compiles, but when I call this method, I get an error which says:

Unable to cast object of type ‘System.Windows.Forms.Button’ to type ‘System.Windows.Forms.TreeView’.

Well obviously, I have some other controls like buttons and etc… I am wondering that what is wrong with my code that comiples but fails in action!

Answer 1

The this.Controls collection contains all controls, not just treeviews and I’m surprised that doesn’t come up with a compile error or even a warning.
You need to check the type of each control before you try and use it as a TreeView:

private void ResetTreeViewColors() { 
    foreach (Control tvc in this.Controls) { 
        if (tvc is TreeView) {
            TreeView tv = (TreeView)tvc;
            foreach(TreeNode tn in tv.Nodes) { 
                tn.BackColor = Color.White; 
                tn.ForeColor = Color.Black; 
            }
        } 
    } 
}